Sperry

• What is the corpus callosum

  a fibre which connects the right and left hemispheres and carries out most of the communication between the two halves/hemispheres
• Background question: lateralisation of function + contralateral control

  1. Sperry wanted to investigate lateralisation of function which is the concept that the two hemispheres of our brain have different functions; the right side controls spatial awareness + left side language
  2. He was also inspired by the concept of contralateral control which is the idea that the brain is crossword meaning the right side of our body is controlled by the left hemisphere + vice versa
• Background question:

  3. To investigate this Sperry had to use people with a severed corpus callosum and whose hemispheres couldn't communicate. Therefore he used people who had a hemisphere deconnection

  4. Sperry therefore aimed to compare the behaviour of split-brain individuals with those with a normal brain to see if there were certain functions they couldn't perform
• What is lateralisation of function

  the 2 hemispheres of the brain have different functions

  -> the left hemisphere is in charge of language: our ability to communicate using spoken words, to process language + to write language

  -> the right hemisphere is in charge of spatial awareness + creativity

  the 2 hemispheres communicate with each other through the corpus callosum so we can perform both sets of functions all of the time
• What is contralateral control

  Brain is cross wired:

  • left hemisphere controls right side of body + all things processed in the left hemisphere display themselves on the right side of the body
• 2 visual fields: each eye has a left + right visual field

  anything seen in the left visual field is processed by the right hemisphere + vice versa (if info is only presented to the left visual field this would be received by the right hemisphere + vice versa due to contralateral control)

  most of the time we see things in both visual fields due to peripheral vision but if our vision was blocked we may only see things through one visual field
• Previous research

  previous research using split-brain animals demonstrated behavioural effects, however, they were not as severely affected as human brains. the monkeys demonstrated difficulties such as slower functioning + worsened memory
• Hemisphere deconnection

  Sperry was interested in the functions of the diff hemispheres in the brain. so she looked at how the responses + behaviours of people who had had a hemispheric reconnection operation (so they had a 'split brain') due to severe epilepsy compares with those with a 'normal' brain. this operation involved their corpus callosum to be severed meaning their was no communication between the hemispheres + the hemispheres are unable to share functions with both sides of the body
• Aim

  to record the psychological effects of hemispheric deconnection and to find evidence for lateralisation of function in 'normal brains'
• Sample

  • 11 men and women who had had the split brain operation who previously had severe epilepsy
  • all Ps had had this procedure at various times before the study, reducing consistency
  • opportunity sample as Sperry used patients who had already had the procedure
• Strengths of the sample

  + males + females used - no gender bias = can generalise findings into lateralisation of function to men + women

  + sample size of 11 split brain people is very representative of split brain people = gives insight into a unique group of people

  + opportunity sampling is quick + easy as Ps already had the procedure before the study = most economical sampling method
• Weaknesses of the sample

  -lack of consistency as the Ps had the hemisphere deconnection at varying times before the study = those who had it earlier may have adapted more + there4 performed better in the tasks

  -all of the Ps had severs epilepsy meaning their brains may have been damaged from seizures which may lead to different findings about lateralisation of function which can't be generalised to 'normal' brains = low population valididty
• Scientific equipment used by researchers

  a tachistoscope which projects visual stimuli (images or words) onto a screen for a specified amount of time

  images were projected to the left or right side of the screen meaning they were seen by the left or right visual field of each eye

  the images projected to the RVF are processed by the left hemisphere + the images projected to the LVF are processed by the right hemisphere
• Research method

  quasi experiment

  IV = whether the Ps had a split brain or not

  DV = their performance on visual + tactile tasks
• Procedure

  1. each participant was studied alone (controls for SDB)
  2. the participant had one eye covered (ensure the visual stimulus is only seen by one visual field + only processed by one hemisphere) + was asked to look at a fixed point in the centre of the screen on the tachistoscope
  3. visual stimuli were then projected onto the screen, either to the right or left visual field
  4. the images were shown for 0.1 seconds each (to control that the Ps had no time to change their visual field)
• Task: One visual field

  • Ps were shown a visual stimulus on the screen in one visual field whilst focusing on a centre point - they saw one image in one visual field for 0.1s
  • they were asked to say or draw what they had seen

  RESULTS: when Ps were shown an image in their LVF it was processed in the right hemisphere (responsible for creativity) there4 they weren't able to say what they saw but they could draw it

  when shown an image in their RVF it was processed in the LVF (responsible for language) so they were able to say + write down what they saw (but no draw it)
• Task: both visual field

  • Ps were shown 2 diff images, one in each visual field at the same time for 0.1
  • they were then asked to say or draw what they had seen

  RESULTS: the image shown in their LVF is processed in the right hemisphere (responsible for creativity/spatial awareness) so they were able to draw the image with their left hand

  the image shown in their RVF was processed in their left hemisphere which is responsible for language there4 they were able to say the image they saw
• Task: Tactile - one hand

  • Ps were given one object in one hand + asked to say or write down what they were holding

  RESULTS: if the item was placed in the Ps right hand then it would be processed in the left hemisphere (responsible for language) therefore they were able to say what they were holding or write it down with their right hand
• Task: Tactile - both hands/dual processing task

  • Ps work with both hands out their sight + are given 2 different objects, one in each hand, then the objects are taken away + put into a pile of other objects
  • Ps are asked to find the object they were originally holding by touch from a pile of items or asked to say what they had just held
• Tactile - both hands/dual processing results

  Participants were able to find the object by touch but only using the hand that was originally holding the item. If the participant was originally holding an item in their left hand, when searching for it with their right hand wouldn't recognise it and therefore would reject the object as if the participant had never held it before + vice versa
• Conclusions

  1. split brain patients appear to have 2 streams of consciousness, each with its own memories, perceptions + impulses: effectively, 2 minds in one body. this supports the argument of lateralisation of function - the idea that diff areas + hemispheres of the brain specialise on diff tasks e.g left side is responsible for language
  2. split brain patients have a lack of cross integration where a second hemisphere doesn't know what the first hemisphere has been doing
• Example Q: outline one conclusion

  One finding from Sperry's study was that when Ps were shown an image in their RVF it was processed in the left hemisphere responsible for language there4 they were able to say what they saw, whereas when shown in the LVF they could only draw it. This allowed Sperry to conclude that split brain patients have 2 independent streams of consciousness which supports the argument of lateralisation of function as the 2 diff hemispheres of the brain specialise in diff tasks
• Further results

  Sperry found the hemisphere deconnection didn't appear to affect Ps intelligence or their personality but the effects of surgery seemed to have affected Ps as they had short-term memory deficits, fatigue more quickly in reading + have limited concentration spans + orientation problems
• Evaluation table

  reliability weakness 2: lack of consistency regarding when Ps had procedure (hemisphere deconnection)

  
• Link to approach Q

  
• Link to key theme Q: what, who, how

  W = aimed to investigate psychological effects of hemisphere deconnection + evidence of lateralisation of function by measuring behavioural differences of people with a severed corpus callosum

  W = 11 men + women who had all had the hemispheric deconnection operation to relieve symptoms of severe epilepsy

  H = Ps performed series of visual + tactile tasks e.g an image was flashed to their RVF for 0.1s + they were asked to name the image
• Link to key theme: finding + link

  F = Sperry found that an image shown in the Ps RVF was processed by the left hemisphere which is responsible for language so they were able to say what they saw

  L = links to regions of brain as Sperry illustrated how the region of the brain, the corpus callosum, plays a major part in normal behaviour + if its severed there are behavioural changes as the 2 hemispheres can't communicate

  OR as it shows evidence for lateralisation of function in a region of the brain, the left and right hemisphere e.g left = language, right = spatial awareness/creativity
• What debates does Sperry link to

  • reductionism = reduces lateralisation of function to biological factors such as the role of the corpus callosum allowing the hemispheres to communicate
  • individual = explains lateralisation of function through the individual differences of the Ps corpus callosum being severed